DIFFERENCES UNDER DIFFERENT CIRCUMSTANCES. 249 



Perhaps, however, it may be asked, Why should the 

 insect change its habits ? Several reasons might be sup;- 

 gested. The prey first selected might be exterminated, 

 or at any rate diminish ia numbers, and, though each 

 sppcies as a general rule confines itself to one special 

 vietiin, some exceptions have already been noticed. 

 For instance, Sphex Jlavipennis habitually preys on a 

 species of grasshopper, but on tiie banks of the Rhone 

 M. Fabre found it, on the contrary, attacking a field 

 cricket, whether from the absence of the grasshopper or 

 not he was unable to determine. 



Take another case. M. Fabre denies* that the 

 different species of Sphex can ever have been derived 

 from one source. Every species now, he observes, has 

 some one victim, some one insect on which it preys, to 

 which it restricts itself, and which the other species do 

 not attack. But " Que chassait, je vous prie, ce proto- 

 type des Sphegiens ? Avait il regime varie ou regime 

 uniforme ? Ne pouvant decider, examiiions les deux 

 cas. 



He begins by supposing that with the ancestor of the 

 Sphex, " Le regime etait varie. J'en felicite hautement 

 ce premier ne des Sphex. II etait dans les meilleures 

 conditions pour laisser descendance prospere." Is it 

 likely then, he says, that they would have limited 

 themselves to one prey, and thus have foolishly 

 diminished their ciiances in life? "Maisnon," he adds, 

 in hi*! lively style, "mes beaux Sphex, vous n'avez pas 

 ete aussi idiots que cela. Si vous etes de nos jours can- 

 tonnes chacun dans un mets de famille, c'est que votre 

 ancetre ne vous a pas enseign^ la variele." 



He then discusses the alternative whether the 

 ♦ " Souv. Entfui., tioisil-me se'rie." 



